Subject Recruitment. Subjects with mild to moderate AD will be recruited from community healthcare providers including internists, primary care physicians, neurologists, and AD subspecialty clinics and IND subject database. Healthy controls will be recruited from our healthy subject database and through advertising. Referred patients will be evaluated by a neurologist at IND. The neurologist will discuss the study procedures and evaluate the patient for eligibility. Written informed consent for the study will be obtained prior to performing any study-related procedures.

Alzheimer's Subject Selection. Subjects who have a clinical diagnosis of mild to moderate Alzheimer's disease will be recruited for this study. The following criteria will be met for inclusion of AD subjects in this study:

• The participant is 50 years or older.
• Written informed consent is obtained.
• Participants have a clinical diagnosis of Alzheimer's disease based on National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS/ADRDA) criteria.
• Mini-Mental Status Exam score < 25.
• Modified Hachinski Ischemia Scale score of ≤ 4.
• Geriatric Depression Scales (GDS) ≤ 10.
• For females, non-child bearing potential or negative urine or blood pregnancy test on day of 123-I AV94 injection.

Alzheimer's subjects will be excluded from participation for the following reasons:

• The subject has signs or symptoms of another neurodegenerative disease including Parkinson's disease, diffuse Lewy body dementia, or history of significant cerebrovascular disease.
• The subject has a clinically significant abnormal laboratory value and/or clinically significant unstable medical or psychiatric illness
• The subject has any disorder that may interfere with drug absorption distribution, metabolism, or excretion (including gastrointestinal surgery).
• The subject has evidence of clinically significant gastrointestinal, cardiovascular, hepatic, renal, hematological, neoplastic, endocrine, neurological, immunodeficiency, pulmonary, or other disorder or disease.
• Pregnancy

Concomitant therapy Patients may remain on a stable dose of anticholinesterase medication during the study. Use of donepezil (Aricept®), rivastigmine (Exelon®), galantamine (Razadyne®), tacrine (Cognex®), and memantine (Namenda®) are permitted during the study. Doses of these compounds must be stable for 2 months prior to the study. At each visit after the screening visit, the investigator will ask the patient whether any medications including OTC medications, were taken since the previous visit.

Use of antipsychotics for agitation and benzodiazepines for insomnia or anxiety is permitted. However, the use of these agents is not permitted within the 8 hours prior to administration of cognitive testing.

Healthy Control Subject Selection. Healthy control subjects who have no neurological disease will be recruited for this study. The following criteria will be met for inclusion of healthy control subjects in this study:

• The participant is 50 years or older.
• Written informed consent is obtained.
• Negative history of neurological or psychiatric illness based on evaluation by a research physician.
• Mini-Mental Status Exam score ≥28.
• For females, non-child bearing potential or negative urine or blood pregnancy test on day of 123-I AV94 injection.

Healthy control subjects will be excluded from participation for the following reasons:

• The subject has a clinically significant abnormal laboratory value and/or clinically significant unstable medical or psychiatric illness.
• The subject has any disorder that may interfere with drug absorption distribution, metabolism, or excretion (including gastrointestinal surgery).
• The subject has evidence of clinically significant gastrointestinal, cardiovascular, hepatic, renal, hematological, neoplastic, endocrine, neurological, immunodeficiency, pulmonary, or other disorder or disease.
• Pregnancy